The present invention relates to a heat-and-electricity supply system for supplying a heat output and an electric output and, more particularly, to a heat-and-electricity supply system in which it is taken into consideration that seasonal fluctuations of the heat output supplied to heat-side equipment are remarkably large.
A heat-and-electricity supply system is known from, for example, Japanese Unexamined Patent Application No. 61-87908, in which a power generator is driven by a gas turbine to generate electric power, thereby providing electric outputs, and in which exhaust gas from the gas turbine is supplied to a waste-heat recovery boiler to generate steam. The steam is supplied to heat-side equipment, thereby providing a heat output. The heat-side equipment is composed of a steam turbine into which steam is introduced to drive a compressor, refrigeration equipment including a compressor as a part of a heat cycle, a heat pump operated with hot water, and the like.
In case of the above known system, the steam generated at the waste-heat recovery boiler is supplied to the heat-side equipment and is utilized as a heat output. However, the load of the heat-side equipment changes greatly with every season, and thus the heat side equipment cannot be used efficiently. For example, when the heat-side equipment is refrigeration equipment and the capacity of the waste-heat recovery boiler is designed according to a high load in the summer season, in the winter season surplus steam occurs due to low load, resulting in a decrease in efficiency. On the other hand, if an amount of fuel fed to the gas turbine is regulated, for the purpose of improving the efficiency in accordance with the load of the seasonal fluctuations in the heat-side equipment, this results in a reduction in the output of the power generator. Moreover, if almost all of the steam is supplied to the heat-side load and consequently the amount of steam introduced into the steam turbine is reduced in the summer season, erosion due to moisture occurs on the discharge side of the steam turbine, so that there is a danger of damage of the steam turbine and the turbine blades.